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Emergence Explained: Entities Getting epiphenomena to do real work Russ Abbott Department of Computer Science, California State University, Los Angeles and The Aerospace Corporation [email protected] Abstract. We apply the notions developed in the preceding paper ([1]) to issues such as: the nature of entities, the fundamental importance of interactions between entities and their environment, the central and often ignored role (especially in computer science) of energy, the aggregation of complexity, and the limitations of modeling.

1 Introduction In [1] we characterized emergent phenomena as phenomena that may be described independently of their implementations. We distinguished between static emergence (emergence that is implemented by energy wells) and dynamic emergence (emergence that is implemented by energy flows). We argued that emergence (of both forms) produces objectively real phenomena (because they are distinguishable by their entropy and mass characteristics) but that interaction among emergent phenomena is epiphenomenal and can always be reduced to the fundamental forces of physics. Our focus in that paper was on the phenomenon of emergence itself. In this paper we explore the two types of emergence, focusing especially on dynamic emergence. 1.1 Entities As human beings we naturally seem to think in terms of entities—things or objects. Yet the question of how one might characterize what should and should not be considered an entity is still unresolved as a philosophical issue. (See [Boyd], [Laylock], [Miller], [Rosen], [Varzi Fall ‘04].) We propose to define a physically based entity as an instance of emergence. This correspond to our intuitive sense for how we think about entities in a great many cases. Physical entities (such as an atom, a molecule, a pencil, a table, a solar system, a galaxy) are all instances of static emergence. These entities are held together in energy wells of various sorts. Biological entities (such as you and I) and social entities (such as a social club, a corporation, or a country) are instances of dynamic emergence. These entities all exist as a result of energy flows of various sorts. (We examine many of the preceding examples in more detail below.) On the other hand, what might be considered conceptual (or Platonic) entities such as numbers, mathematical sets (and other mathematical constructs), properties, relations, propositions, categories named by common nouns (such as “cat”), and ideas in general are not instances of emergence. Nor are literary products such as poems and novels, scientific papers, or computer programs (when considered as texts). Time instances (e.g., midnight 31 December 1999), durations (e.g., a minute), and segments (e.g., the 20 th century) are also not instances of emergence. Neither are the comparable constructs with reEmergence Explained

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spect to space and distance. An entity as we define it always consists at least in part of matter—which is arranged to implement some independently describable abstraction. Since none of the preceding conceptual entities involve matter, none of them are physical entities according to our definition.1 1.2 What does it mean to describe an entity? As suggested by our definition of emergence, there are two ways to describe an entity. 1. In terms of its interaction with its environment (including its response to measurement instruments)—i.e., a description given in terms of its observed (or desired) properties and behavior. When done more rigorously, this becomes a formal specification. 2. In terms of its internal structure and operation, i.e., its implementation. The agenda of most of science—and of petty reductionism2 in particular—has been to show how an understanding of entities from the second perspective explains why they appear and behave as they do from the first perspective. In this paper we take a closer look at the first perspective focusing in particular on how entities interact with their environment. An entity’s interaction with its environment is particularly important for dynamic entities, which depend on their environments to provide the energy that enable them to persist.

2 Static entities Statically emergent entities (static entities for short) are created when the fundamental forces of nature bind matter together. The nucleus of any atom (other than simple Hydrogen, whose nucleus consist of a single proton) is a static entity. It results from the application of the strong nuclear force, which binds the nucleons together in the nucleus. Similarly any atom (the nucleus along with the atom’s electrons) is also a static entity. An atom is a consequence of the electromagnetic force, which binds the atom’s electrons to its nucleus. Molecules are also bound together by the electromagnetic force. On a much larger scale, astronomical bodies, e.g., the earth, are bound together by gravity, as are solar systems and galaxies. Like all entities, static entities have properties which may be described independently of how they are constructed. As Weinberg [W] points out, “a diamond [may be described in terms of its hardness even though] it doesn't make sense to talk about the hardness … of individual ‘elementary’ particles.” The hardness of a diamond may be characterized and measured independently of how diamonds achieve that property—which as Weinberg also points out is a consequence of how diamonds are implemented, namely, their “carbon atoms … can fit together neatly.” A distinguishing feature of static entities (as with static emergence in general) is that the mass of any one of them is strictly smaller than the sum of the masses of its components. This may be seen most clearly in nuclear fission and fusion, in which one starts and ends with the same number of atomic components—electrons, protons, and neutrons—but 1 2

We explore the relationship between ideas and computation in [If a Tree]. Recall Weinberg characterization of petty reductionism as the “doctrine that things behave the way they do because of the properties of their constituents.”

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which nevertheless converts mass into energy. This raises the obvious question: which mass was converted to energy? The answer has to do with the strong nuclear force, which implements what is called the “binding energy” of nucleons within a nucleus. For example, a helium nucleus (also known as an alpha particle, two protons and two neutrons bound together), which is one of the products of hydrogen fusion, has less mass than the sum of the masses of the protons and neutrons that make it up.3 The missing mass is released as energy. The same entity-mass relationship holds for all static entities. An atom or molecule has less mass (by a negligible but real amount) than the sum of the masses of its components taken separately. The solar system has less mass (by a negligible but real amount) than the mass of the sun and the planets taken separately. Thus the entropy of these entities is lower than the entropy of the components as an unorganized collection. In other words, a static entity is distinguishable by the fact that it has lower mass and lower entropy than its components taken separately. Static entities exist in what is often called an energy well; they require energy to pull their components apart. Static entities are also at an energy equilibrium. Manufactured or constructed artifacts exhibit static emergence. The binding force that holds manufactured static entities together is typically the electromagnetic force, which we exploit when we use nails, glue, screws, etc. to bind static entities together into new static entities. A house, for example, has the statically emergent property number-of-bedrooms, which is a property of (a way of describing) the house from the entity perspective. A house implements the property of having a certain number of bedrooms by the way in which it is constructed from its components. A static entity consists of a fixed collection of components over which it supervenes. By specifying the states and conditions of its components, one fixes the properties of the entity. But static entities that undergo repair and maintenance, such as houses, no longer consist of a fixed collection of component elements thereby raising the question of whether such entities really do supervene over their components. We resolve this issue when we discuss Theseus’ ship.

3 Dynamic entities Dynamic entities are instances of dynamic emergence. Dynamic emergence occurs when energy flows through and modifies an open system. As in the case with all emergence, dynamic emergence results in the organization of matter in a way that differs from how it would be organized without the energy flowing through it. That is, dynamic entities have properties as entities that may be described independently of how those properties are implemented. Dynamic entities include dissipative, biological, and social entities—and as we discuss below, hurricanes. In many but not necessarily all cases, the very existence of the dynamic entity as an entity—its reduced entropy and its increased mass—depends on the flow of energy. In the case of dissipative entities, the entity would exist as a static entity even when energy is not flowing through it.

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It turns out that iron nuclei lack the most mass. Energy from fusion is possible for elements lighter than iron; energy from fission is possible for elements heavier than iron.

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3.1 Dissipative entities We begin with the relatively simple case in which a static entity becomes a dissipative entity. In [Prigogine] (and elsewhere) Prigogine discusses what he calls dissipative structures. A dissipative structure is an organized pattern of activity within a constrained environment that is produced when an external source of energy is introduced into the constrained environment. A dissipative structure is so named because in maintaining its pattern of activity it dissipates the energy supplied to it. A static entity becomes dissipative when a stream of energy is pumped into it in such a way that the energy disturbs the internal structure of the entity and then dissipates before the static entity’s structure is destroyed. Musical instruments offer a nice range of examples. Some are very simple (direct a stream of air over the mouth of a soda bottle); others are more acoustically complex (a violin). All are static entities that emit sounds when energy is pumped into them. Another commonly cited example is the collection of Rayleigh-Bénard convection patterns that form in a confined liquid when one surface is heated and the opposite surface is kept cool. (See Figure 1.) For a much larger example, consider how water is distributed over the earth. Water is transported from place to place via processes that include evaporation, atmospheric weather system movements, precipitation, groundwater flows, ocean current flows, etc. Taken as a whole, these cycles may be understood as a dissipative structure which is shaped by gravity and the earth’s fixed geographic structure and driven primarily by solar energy, which is pumped into the earth’s atmosphere. Our notion of a dissipative entity is broad enough to include virtually any energy-consuming device. Consider a digital clock. It converts an inflow of energy into an ongoing series of structured activities—resulting in the display of the time. Does a digital clock qualify as a dissipative entity? One may argue that since the design of a digital clock limits the ways in which it can respond to the energy inflow it receives it should not be characterized as a dissipative entity. But any static entity has only a limited number of ways in which it can respond to an inflow of energy. We suggest that it would be virtually impossible to formalize a principled distinction between Rayleigh-Bénard convection cycles and the structured activities within a digital clock.4, 5 Just as emergent phenomena are typically limited to feasibility ranges, dissipative entities also operate in distinct ways within various energy intensity ranges. Blow too gently into a recorder; nothing happens. Blow too strongly; the recorder will break. Within the range in which sounds are produced, different intensities will produce either the intended sounds or unintended squeaks. Thus dissipative entities exhibit phases and phase transitions that depend on the intensity of the energy they encounter. The primary concern about global warming, for example, is not that the temperature will rise by a degree or two—although the melting of the ice caps is potentially destructive—but the possibility that a phase transition will occur and that the overall global climate structure, including 4

Another common example of a dissipative structure is the Belousov-Zhabotinsky (BZ) reaction, which in some ways is a chemical watch. We designed digital clocks to tell time. We didn’t design BZ reactions to tell time. Yet in some sense they both do. That one surprises us and the other doesn’t shouldn’t mislead us into putting them into different categories of phenomena.

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In all our examples, the form in which energy is delivered also matters. An electric current will produce different effects from a thermal energy source when introduced into a digital clock and a Rayleigh-Bénard device.

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atmospheric and oceanic currents, will change disastrously. When energy is flowing through it, a dissipative entity is by definition far from equilibrium. So a dissipative entity is a static entity that is maintained in a far-from-equilibrium state. 3.2 Hurricanes as dynamic entities Most dynamic entities are biological or social, but there are some naturally occurring dynamic entities that are neither. Probably the best known are hurricanes. A hurricane operates as a heat engine in which condensation—which replaces combustion as the source of heat—occurs in the upper atmosphere. A hurricane involves a greater than normal pressure differential between the ocean surface and the upper atmosphere. That pressure differential causes warm moist surface air to rise. When the moisture-laden air reaches the upper atmosphere, which is cooler, it condenses, releasing heat. The heat warms the air and reduces the pressure, thereby maintaining the pressure differential.6 (See Figure 3.) Hurricanes are objectively recognizable as entities. They have reduced entropy—hurricanes are quite well organized—and because of the energy flowing through them, they have more mass than their physical components (the air and water molecules making them up) would have on their own. Hurricanes illustrate the case of a dynamic entity with no static structure. When a hurricane loses its external source of energy—typically by moving over land—the matter of which it’s composed is no longer bound together into an organized structure. The hurricane’s entropy rises and its excess mass—in the form of the energy flowing through it—dissipates until it no longer exists as an entity. 3.3 Petty reductionism fails—for all practical purposes Hurricanes illustrate a difficulty with petty reductionism. Petty reductionism is another way of saying that an entity supervenes over the matter of which it is composed: fixing the properties of the matter of which an entity is composed fixes the properties of the entity itself.7 When one considers dynamic entities such as a hurricane a problem arises. From moment to moment new matter is incorporated into a hurricane and matter then in a hurricane leaves it. Consider the smallest collection of matter over which a hurricane supervenes. Call that the hurricane’s supervenience base. A hurricane’s supervenience base consists of the entire collection of matter that is part of a hurricane over its lifetime. On intuitive grounds it would seem that a hurricane’s supervenience base must be significantly larger than the amount of matter that composes a hurricane at any given moment. Because a hurricane’s supervenience base is so much larger than the matter that makes it up at any moment the fact a hurricane supervene over its supervenience base is not very useful. Other than tracking all the matter in a hurricane’s supervenience base, there is no easy reducibility equation that maps the properties of a hurricane’s supervenience base onto properties of the hurricane itself.

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A characterization of a hurricane as a vertical heat engine may be found in Wikipedia. (URL as of 9/1/2005: http://en.wikipedia.org/wiki/Hurricane.) The hurricane description is paraphrased from NASA, “Hurricanes: The Greatest Storms on Earth,” (URL as of 3/2005 http://earthobservatory.nasa.gov/Library/Hurricanes/.)

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Recall that a set of higher level predicates is said to supervene over a set of lower level predicates if a configuration of truth values for the lower level predicates determines the truth values for the higher level predicates. We are using the term supervene loosely to say that an entity supervenes over its components.

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Furthermore, the longer a hurricane persists, the larger its supervenience base. Much of the matter in a hurricane’s supervenience base is likely also to be included in the supervenience bases of other hurricanes. Like Weinberg’s example of quarks being composed (at least momentarily) of protons, hurricanes are at least partially composed of each other. Thus petty reductionism is not particularly useful for macro-level dynamic entities which cycle matter through themselves—as most dynamic entities do. 3.4 Biological and social dynamic entities Biological and social entities also depend on external energy sources. Photosynthesizing plants depend on sunlight. Other biological entities depend on food resources and mechanisms to oxidize them.. Social entities may be organized along a number of different lines. In modern economies, money is a proxy for energy. Economic entities persist only so long as the amount of money they take in exceeds the amount of money they expend. Political entities depend on the energy contributed—either voluntarily, through taxes, or conscription—of their subjects. Smaller scale social entities such as families, clubs, etc., depend on the contributions of their member. The contributions may be voluntary, or they may result from implicit (social norms) or explicit coercion. No matter the source of the energy or the nature of the components, biological and social entities follow the same pattern we saw with hurricanes. •

They have reduced entropy (greater order) than their components would have on their own.

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They depend on external sources of energy to stay in existence.

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The material that makes them up changes as time passes. Their supervenience bases are generally much larger than the material of which they are composed at any moment. The longer a dynamic entity persists, the greater the difference. Petty reductionism fails unless it becomes a historical narrative. One can tell the story of a corporation or a country as a history that depends in part on who its employees or citizens are at various times. One would have a very difficult time constructing an equation that maps, for example, a corporation’s or a country’s supervenience base (which includes its employees or citizens over all time) to its state at any moment unless that mapping were in effect a historical record. Thus even though dynamic entities persist in time, and even though the properties of dynamic entities are a function of the properties of their components at any moment, since the components of which a dynamic entity is composed change from time to time, there is no direct way to map the properties of the components a dynamic entity will have over its lifetime to the moment-to-moment properties of the entity itself except as a narrative, i.e., a story which describes which elements happen to become incorporated into the dynamic entity at various moments during its lifetime. All entities are subject to the effect of interactions with elements they encounter in their environments. Dynamic entities are doubly vulnerable. They are also subject to having their components replaced by other components. To persist they must have defenses

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against infiltration by elements that once incorporated into their internal mechanisms may lead to their weakening or destruction. 3.5 Theseus’ ship The notion of a social dynamic entity can help resolve the paradox of Theseus’s ship, a mythical ship that was maintained (repaired, repainted, etc.) in the harbor at Athens for so long that all of its original material was replaced. The paradox arises when we think of Theseus’ ship as identical to the material of which it is composed at any moment. Any modification to that ship, e.g., new paint, will change the material of which the ship is composed, and the repaired ship will consist of somewhat different material than the ship consisted of before it was painted. So is the repainted ship “the same ship” as it was before it was painted? This cycling of material through an entity wasn’t a problem when we were discussing hurricanes or social or biological entities. In those cases we thought of the entity as including not only its momentary physical components. The entity also included the energy that was flowing through it along with means to slough off old material and to incorporate new material into its structure. To apply the same perspective to Theseus’ ship, think of the physical ship along with the maintenance process as a social entity. That social entity, like all social entities, is powered by an external energy source. (Since entity the maintenance entity is a governmental or societal function, the energy source is either voluntary, conscripted, or taxation.) The ship maintenance entity uses its energy source to do the maintenance work on the ship according to whatever procedures it follows. The maintenance entity continues to persist and to maintain the physical ship as long as its energy source continues to supply it with energy. Just as the material that makes up a hurricane changes from time to time and the people who are employed by a business change from time to time (as does its physical facilities and other components), the physical ship also changes from time to time. But the ship maintenance entity, like a company, persists over time. [Sidebar] Autonomy The notion of an autonomy seems central to how we look at the world. Most people will acknowledge that the kinds of entities that the biological and social sciences deal with seem somehow different from those of physics and chemistry. A major part of that difference is the apparent ability of those entities to act on their own, i.e., their autonomy. For millennia we have found it convenient to partition the world into two realms: the animate and the inanimate. Elements of the inanimate world are ruled by, are subject to, and are often victims of external forces. Elements of the animate world are capable of autonomous action and seem to have some control over their fate. Recall that this is why Brownian motion posed such a problem: how can inanimate particles look so much like they are moving autonomously? For the past half-millennium civilization has pursued, with significant success, the dream of creating autonomous sources of action. We have built machines about which it can be said that to varying degrees they act on their own. We do not yet confuse our machines with biological life, and we have not yet managed to construct biological life “from scratch.” But the boundaries between human artifacts, natural biological life, and hybrids Emergence Explained

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of the two are becoming more and more subtle—and they are likely to disappear within the lifetimes of many of us. So, what do we mean by autonomy? In non-political contexts, the term autonomous is taken to mean something like not controlled by outside forces. But any material entity is subject to outside, i.e., physical, forces. Nothing is free from the laws of physics. Instead of defining autonomy to require imperviousness to outside forces, it makes more sense to understand autonomy to imply the ability to control—at least to some extent—how an entity is affected by outside forces. Thus we suggest that an entity is autonomous to the extent that it shapes the way it is affected by outside forces. But this is another way of looking at how we have defined a dynamic entity. Every dynamic entity is autonomous to some degree since they shape how the energy that flows through them is used. Most biological and social entities do more than just shape the “raw” energy flows that they encounter. Most biological and social entities are able to acquire energy in some “frozen” form (such as food or money8) and to convert it to energy as needed. Also, these entities often have an ability to seek out energy in their environments rather than just waiting for energy to be pumped into them. Furthermore, many of these entities are capable of using many forms of energy and energy supplied at many levels of intensity. Thus the notion of autonomy seems to depend on the flexibility with which a dynamic entity is able to deal with energy. It seems appropriate that autonomy should be tied to a notion as fundamental as energy. In the previous article we noted that causality is always reducible to the primitive forces of physics. An entity’s autonomy is therefore a measure of the extent to which it is able to direct and control those fundamental forces—and hence the extent to which it can influence causal relationships. [Sidebar] Minimal dynamic entities In [Kauffman] Kauffman asks what the basic characteristics are of what he calls autonomous agents. He suggests that the ability to perform a thermodynamic (Carnot engine) work cycle is fundamental. In what may turn out to be the same answer we suggest looking for the minimal biological organism that perpetuates itself by consuming energy. Bacteria seem to be too complex. Viruses and prions don’t consume energy. Hurricanes aren’t biological. Is there anything in between? Such a minimal entity may help us understand the yet-to-be-discovered transition from the inanimate to the animate. Since self-perpetuation does not imply reproduction (as hurricanes illustrate), simple selfperpetuating organisms may not be able to reproduce. That means that if they are to exist, it must be relatively easy for them to come into being directly from inorganic materials. Self-perpetuating organisms may not include any record—like DNA—of their design (as hurricanes again illustrate). One wouldn’t expect to see evolution among such organisms —at least not evolution that depends on modifications of such design descriptions. [Sidebar] Thermodynamic computing: nihil ex nihilo In Computer Science we assume that one can specify a Turing Machine, a Finite State Automaton, a Cellular Automaton, or a piece of software, and it will do its thing—for free. Turing machines run for free. Cellular Automata run for free. Gliders run for free. 8

The maxim follow the money is really advising that one find energy sources and sinks.

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Software in general runs for free. Even agents in agent-based models run for free. 9. Although that may be a useful abstraction, we should recognize that we are leaving out something important. In the real world one needs energy to drive processes. To run real software in the real world requires a real computer, which uses real energy. A theory of thermodynamic computation is needed to integrate the notions of energy, entities, and computing. The problem is that the real energy that drives software is not visible to the software itself. Software does not have to pay its own energy bill. Until we find a way to integrate the real energy cost of running software into the software itself, we are unlikely to build a successful artificial life model.

4 The environment Consider the following from Weinberg. [A]part from historical accidents that by definition cannot be explained, the [human] nervous system [has] evolved to what [it is] entirely because of the principles of macroscopic physics and chemistry, which in turn are what they are entirely because of the principles of the standard model of elementary particles. Note Weinberg’s reference to historical accidents—which we also saw earlier, in his definition of grand reductionism. Grand reductionism is … the view that all of nature is the way it is (with certain qualifications about initial conditions and historical accidents) because of simple universal laws, to which all other scientific laws may in some sense be reduced. Even though Weinberg gives historical accidents as important a role in shaping the world as he does the principles of physics, he does so grudgingly, seemingly attempting to dismiss them in a throw-away subordinate clause. This is misleading, especially given Weinberg’s example—evolution. Contrary to his implication, the human nervous system (and the designs of biological organisms in general) evolved as they did not primarily because of the principles of physics and chemistry but primarily because of the environment in which that evolution took place. Biological systems are open; they depend on their environment for the energy that perpetuates them. Biological organisms must have designs that extract energy from the environment. Those designs are limited by the ways in which energy is available in the environment. Physics and chemistry limit the mechanisms those designs may employ, but how the designs employ those mechanisms to perform a function depends on the environment within which the mechanisms must operate. As Jakobsson put it recently [Jakobsson] “Biology is concerned equally with mechanism and function.” This really is not so foreign to elementary particle physics. The Pauli exclusion principle, which prevents two fermions from occupying the same quantum state, formalizes a constraint the environment imposes on elementary particles.10 9

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Many agent-based and artificial life models acknowledge the importance of energy by imposing an artificial price for persistence, but we are not aware of any in which the cost of existence is fully integrated into the functioning of the entity. This was pointed out to me by Eshel Ben-Jacob [private communication].

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Functionalism too has an environmental focus. By definition functionality is a relationship between something and its environment. As Fodor points out, references to can openers, mousetraps, camshafts, calculators and the like bestrew the pages of functionalist philosophy. To make a better mousetrap is to devise a new kind of mechanism whose behavior is reliable with respect to the high-level regularity “live mouse in, dead mouse out.” Thus although neither Weinberg nor Fodor focuses on this issue explicitly—in fact, they both tend to downplay it—they both apparently agree that the environment within which something exists is important. 4.1 What dynamic entities do vs. how dynamic entities work In his talk at the 2006 Understanding Complex Systems Symposium Eric Jakobsson made the point that biology must be equally concerned with what organisms do in their worlds and the mechanisms that allow them to do it. 4.2 Stigmergy Once one has autonomous entities (or agents) that persist in their environment, the ways in which complexity can develop grows explosively. Prior to agents, to get something new, one had to build it as a layer on top of some existing substrate. As we have seen, nature has found a number of amazing abstractions along with some often surprising ways to implement them. Nonetheless, this construction mechanism is relatively ponderous. Layered hierarchies of abstractions are powerful, but they are not what one might characterize as lightweight or responsive to change. Agents change all that. Half a century ago, Pierre-Paul Grasse invented [Grasse] the term stigmergy to help describe how social insect societies function. The basic insight is that when the behavior of an entity depends to at least some extent on the state of its environment, it is possible to modify that entity’s behavior by changing the state of the environment. Grasse used the term “stigmergy” for this sort of indirect communication and control. This sort of interplay between agents and their environment often produces epiphenomenal effects that are useful to the agents. Often those effects may be understood in terms of formal abstractions. Sometimes it is easier to understand them less formally. Two of the most widely cited examples of stigmergic interaction are ant foraging and bird flocking. In ant foraging, ants that have found a food source leave pheromone markers that other ants use to make their way to that food source. In bird flocking, each bird determines how it will move at least in part by noting the positions and velocities of its neighboring birds. The resulting epiphenomena are that food is gathered and flocks form. Presumably these epiphenomena could be formalized in terms of abstract effects that obeyed a formal set of rules—in the same way that the rules for gliders and Turing Machines can abstracted away from their implementation by Game of Life rules. But often the effort required to generate such abstract theories doesn’t seem worth the effort—as long as the results are what one wants. Here are some additional examples of stigmergy. Emergence Explained

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When buyers and sellers interact in a market, one gets market epiphenomena. Economics attempts to formalize how those interactions may be abstracted into theories.

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We often find that laws, rules, and regulations have both intended and unintended consequences. In this case the laws, rules, and regulations serve as the environment within which agents act. As the environment changes, so does the behavior of the agents.

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Both sides of the evo-devo (evolution-development) synthesis [Carroll] exhibit stigmergic emergence. On the “evo” side, species create environmental effects for each other as do sexes within species.

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The “devo” side is even more stigmergic. Genes, the switches that control gene expression, and the proteins that genes produce when expressed all have environmental effects on each other.

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Interestingly enough, the existence of gene switches was discovered in the investigation of another stigmergic phenomenon. Certain bacteria generate an enzyme to digest lactose, but they do it only when lactose is present. How do the bacteria “know” when to generate the enzyme? It turns out to be simple. The gene for the enzyme exists in the bacteria, but its expression is normally blocked by a protein that is attached to the DNA sequence just before the enzyme gene. This is called a gene expression switch. When lactose is in the environment, it infuses into the body of the bacteria and binds to the protein that blocks the expression of the gene. This causes the protein to detach from the DNA thereby “turning on” the gene and allowing it to be expressed. The lactose enzyme switch is a lovely illustration of stigmergic design. As we described the mechanism above, it seems that lactose itself turns on the switch that causes the lactose-digesting enzyme to be produced. If one were thinking about the design of such a system, one might imagine that the lactose had been designed so that it would bind to that switch. But of course, lactose wasn’t “designed” to do that. It existed prior to the switch. The bacteria evolved a switch that lactose would bind to. So the lactose must be understood as being part of the environment to which the bacteria adapted by evolving a switch to which lactose would bind. How clever; how simple; how stigmergic!

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Cellular automata operate stigmergically. Each cell serves as an environment for its neighbors. As we have seen, epiphenomena may include gliders and Turing Machines.

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Even the operation of the Turing Machine as an abstraction may be understood stigmergically. The head of a Turing Machine (the equivalent of an autonomous agent) consults the tape, which serves as its environment, to determine how to act. By writing on the tape, it leaves markers in its environment to which it may return—not unlike the way foraging ants leave pheromone markers in their environment. When the head returns to a marker, that marker helps the head determine how to act at that later time.

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In fact, one may understand all computations as being stigmergic with respect to a computer’s instruction execution cycle. Consider the following familiar code fragment. temp:= x; x := y; y := temp; The epiphenomenal result is that x and y are exchanged. But this result is not a consequence of any one statement. It is an epiphenomenon of the three statements being executed in sequence by a computer’s instruction execution cycle. Just as there in nothing in the rules of the Game of Life about gliders, there is nothing in a computer’s instruction execution cycle about exchanging the values of x and y—or about any other algorithm that software implements. Those effects are all epiphenomenal.

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The instruction execution cycle itself is epiphenomenal over the flow of electrons through gates—which knows no more about the instruction execution cycle than the instruction execution cycle knows about algorithms.

In all of the preceding examples it is relatively easy to identify the agent(s), the environment, and the resulting epiphenomena. 4.3 Design and evolution It is not surprising that designs appear in nature. It is almost tautologous to say that those things whose designs work in the environments in which they find themselves will persist in those environments. This is a simpler (and more accurate) way of saying that it is the fit—entities with designs that fit their environment—that survive. 4.4 The accretion of complexity An entity that suits its environment persists in that environment. But anything that persists in an environment by that very fact changes that environment for everything else. This phenomenon is commonly referred to as an ever changing fitness landscape. What has been less widely noted in the complexity literature is that when something is added to an environment it may enable something else to be added latter—something that could not have existed in that environment prior to the earlier addition. This is an extension of notions from ecology, biology, and the social sciences. A term for this phenomenon from the ecology literature, is succession. (See, for example, [Trani].) Historically succession has been taken to refer to a fairly rigid sequence of communities of species, generally leading to what is called a climax or (less dramatically) a steady state. Our notion is closer to that of bricolage, a notion that originated with the structuralism movement of the early 20th century [Wiener] and which is now used in both biology and the social sciences. Bricolage means the act or result of tinkering, improvising, or building something out of what is at hand.

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In genetics bricolage refers to the evolutionary process as one that tinkers with an existing genome to produce something new. [Church]. John Seely Brown, former chief scientist for the Xerox Corporation and former director  of the Xerox Palo Alto Research Center captured its sense in a recent talk. [W]ith bricolage you appropriate something. That means you bring it into your space, you tinker with it, and you repurpose it and reposition it. When you repurpose something, it is yours.11 Ciborra [Ciborra] uses bricolage to characterize the way that organizations tailor their information systems to their changing needs through continual tinkering. This notion of building one thing upon another applies to our framework in that anything that persists in an environment changes that environment for everything else. The Internet provides many interesting illustrations. •

Because the Internet exists at all, access to a very large pool of people is available. This enabled the development of websites such as eBay.

•

The establishment of eBay as a persistent feature of the Internet environment enabled the development of enterprises whose only sales outlet was eBay. These are enterprises with neither brick and mortar nor web storefronts. The only place they sell is on eBay. This is a nice example of ecological succession.

•

At the same time—and again because the Internet provides access to a very large number of people—other organizations were able to establish what are known as massively multi-player online games. Each of these games is a simulated world in which participants interact with the game environment and with each other. In most of these games, participants seek to acquire virtual game resources, such as magic swords. Often it takes a fair amount of time, effort, and skill to acquire such resources.

•

The existence of all of these factors resulted, though a creative leap, in an eBay market in which players sold virtual game assets for real money. This market has become so large that there are now websites dedicated exclusively to trading in virtual game assets. [Wallace]

•

BBC News reported [BBC] that there are companies that hire low-wage Mexican and Chinese teenagers to earn virtual assets, which are then sold in these markets. How long will it be before a full-fledged economy develops around these assets? There may be brokers and retailers who buy and sell these assets for their own accounts even though they do not intend to play the game. (Perhaps they already exist.) Someone may develop a service that tracks the prices of these assets. Perhaps futures and options markets will develop along with the inevitable investment advisors.

11

In passing, Brown claims that this is how most new technology develops. [T]hat is the way we build almost all technology today, even though my lawyers don't want to hear about it. We borrow things; we tinker with them; we modify them; we join them; we build stuff.

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The point is that once something fits well enough into its environment to persist it adds itself to the environment for everything else. This creates additional possibilities and a world with ever increasing complexity. In each of the examples mentioned above, one can identify what we have been calling an autonomous entity. In most cases, these entities are self-perpetuating in that the amount of money they extract from the environment (by selling either products, services, or advertising) is more than enough to pay for the resources needed to keep it in existence. In other cases, some Internet entities run on time and effort contributed by volunteers. But the effect is the same. As long as an entity is self-perpetuating, it becomes part of the environment and can serve as the basis for the development of additional entities. 4.5

Increasing complexity increasing efficiency, and historical contingency The phenomenon whereby new entities are built on top of existing entities is now so widespread and commonplace that it may seem gratuitous even to comment on it. But it is an important phenomenon, and one that has not received the attention it deserves. Easy though this phenomenon is to understand once one sees it, it is not trivial. After all, the second law of thermodynamics tells us that overall entropy increases and complexity diminishes. Yet we see complexity, both natural and man made, continually increasing. For the most part, this increasing complexity consists of the development of new autonomous entities, entities that implement the abstract designs of dissipative structures. This does not contradict the Second Law. Each autonomous entity maintains its own internally reduced entropy by using energy imported from the environment to export entropy to the environment. Overall entropy increases. Such a process works only in an environment that itself receives energy from outside itself. Within such an environment, complexity increases. Progress in science and technology and the bountifulness of the marketplace all exemplify this pattern of increasing complexity. One might refer to this kind of pattern as a metaepiphenomenon since it is an epiphenomenon of the process that creates epiphenomena. This creative process also tends to exhibit a second meta-epiphenomenon. Overall energy utilization becomes continually more efficient. As new autonomous entities find ways to use previously unused or under-used energy flows (or forms of energy flows that had not existed until some newly created autonomous entity generated them, perhaps as a waste product), more of the energy available to the system as a whole is put to use. The process whereby new autonomous entities come into existence and perpetuate themselves is non-reductive. It is creative, contingent, and almost entirely a sequence of historical accidents. As they say, history is just one damn thing after another—to which we add, and nature is a bricolage. We repeat the observation Anderson made more than three decades ago. The ability to reduce everything to simple fundamental laws [does not imply] the ability to start from those laws and reconstruct the universe.

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4.6 Evolutionary environments • Access to a supply of externally provided energy and means for exchanging it. All such environments are what is commonly known as far from equilibrium systems in that externally supplied energy continually flows through them. The overall creative process can be summarized as consisting of finding increasingly innovative ways of using the available energy. To facilitate this process, mechanisms must be available to support the fungibility of energy—and its proxies such as money, power, and attention. •

Standards. New products, services, and other items are almost always created (composed) from existing products, services, and other items. Composition is greatly facilitated when the elements to be composed adhere to widely accepted standards.

•

Communication and transportation infrastructures. Communication and transportation infrastructures facilitate the exchange/transfer/flow of (a) information throughout the environment and (b) energy (in one direction) and (c) products and services (in the other) among trading partners.

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A reasonable level of confidence in the stability and continuity of the products and services installed in the environment. Mechanisms must be available to allow agreements to be made and for installed products and services to be relied upon.

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Minimum overhead. Cultural or other mechanisms must exist to discourage corruption along with enforcement mechanisms to make it harder to siphon off energy flows for non-productive uses. More generally, the environment must incorporate mechanisms that minimize the overhead of participating.

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Both (a) centralized but quasi-democratic and transparent governance of the overall system, its infrastructure, and the standards making process and (b) decentralized overall control (“power to the edge”) in which as much autonomy as possible is ceded to environment participants.

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Mechanisms that ensure that a certain amount of the available energy is devoted to the exploration of the space of new possibilities.

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Mechanisms that allow new products and services to be developed and installed in the environment and then made known to other participants in the environment.

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A (primarily, but perhaps not exclusively) bottom-up (i.e., market-like) means for allocating energy (or its proxies) according to usefulness: the more (less) useful a product or service is found to be (according to actual usage), the more (fewer) resources it will have at its disposal. All of the participants in the environment must be self-sustaining in terms of their overall energy transactions. This is possible because the environment is based on an available external source of “free” energy.

•

An ability to form communities of interest (formal, informal, voluntary, and feebased) to facilitate the sharing of information, experience, and expertise. The value of shared information is typically enhanced when it is shared in groups.

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Both (a) sufficient stability of the overall environment that participants can establish regularized modes of participation and (b) (generally collaborative) means to allow the environment to evolve as conditions change.

5 Entities, emergence, and science 5.1 Entities and the sciences One reason that the sciences at levels higher than physics and chemistry seem somehow softer than physics and chemistry is that they work with autonomous entities, entities that for the most part do not supervene over any conveniently compact collection of matter. Entities in physics and chemistry are satisfyingly solid—or at least they seemed to be before quantum theory. In contrast, the entities of the higher level sciences are not defined in terms of material boundaries. These entities don’t exist as stable clumps of matter; it’s hard to hold them completely in one’s hand—or in the grip of an instrument. The entities of the special sciences are objectively real—there is some objective measure (their reduced entropy relative to their environment) by which they qualify as entities. But as we saw earlier, the processes through which these entities interact and by means of which they perpetuate themselves are epiphenomenal. Even though the activities of higher level entities may be described in terms that are independent of the forces that produce them (recall that this is our definition of epiphenomenal), the fundamental forces of physics are the only forces in nature. There is no strong emergence. All other force-like effects are epiphenomenal. Consequently we find ourselves in the position of claiming that the higher level sciences study epiphenomenal interactions among real if often somewhat ethereal entities. “Of course,” one might argue, “one can build some functionality that is not a logical consequence of its components.” Fodor’s simplest functionalist examples illustrate this phenomenon. The physics underlying the components of a mousetrap won’t tell you that when you put the components together in a particular way the result will trap a mouse. The reason why rules of fundamental physics cannot tell you that is because mice simply are not a part of the ontology of fundamental physics in the same way as Turing Machines are not part of the ontology of the Game of Life. If an object is designed to have a function, then if its design works, of course it has that function—even if, as is likely, that function is logically independent of the laws that govern the components. We build objects with particular functions all the time. It’s called ingenuity—or simply good software or engineering design. Even chimpanzees build and use tools. They use stems to extract termites from mounds, they use rocks to open nuts, and perhaps even more interestingly, they “manufacture” sponges by chewing grass roots until they become an absorbent mass. [Smithsonian] But of course from the perspective of fundamental physics, stems are not probes; rocks are not hammers; and roots are not sponges. To be clear about this point, when we say that the functionality of a designed element is logically independent of some lower level domain we are not saying that the higher level functionality is completely unconstrained by the lower level framework. Of course a Turing Machine emulation is constrained by the rules of the Game of Life, and the functionEmergence Explained

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ing of a mouse trap is constrained by the laws of physics. But in both cases, other than those constraints, the functionality of the designed artifact is logically independent of the laws governing the underlying phenomena. Typically, the functionality of the designed artifact is expressed in terms that are not even a present in the ontological framework of the lower level elements. The question we pose in this subsection (and answer in the next) is whether such logically independent functionality occurs “in nature” at an intermediate level, at the level of individual things. Or does this sort of phenomenon occur only in human (or chimpanzee) artifacts? Given the current debate (at least in the United States) about evolution, one might take this as asking whether the existence of a design always implies the existence of a (presumably intelligent) designer.

6 Some practical considerations 6.1 Emergence and software As noted earlier, the computation that results when software is executed is emergent. It is an epiphenomenon of the operation of the (actual or virtual) machine that executes the software. Earlier we defined emergence as synonymous with epiphenomenon. At that time we suggested that formalizable epiphenomena are often of significant interest. We also said that formalization may not always be in the cards. Software, which one would imagine to be a perfect candidate for formalization, now seems to be a good example of an epiphenomenon that is unlikely to be formalized. It had once been hoped that software development could evolve to a point at which one need only write down a formal specification of what one wanted the software to do. Then some automatic process would produce software that satisfied that specification. That dream now seems quite remote. Besides the difficulty of developing (a) a satisfactory specification language and (b) a system that can translate specifications written in such a language into executable code, the real problem is that it has turned out to be at least as difficult and complex to write formal specifications as it is to write the code that produces the specified results. Even if one could write software by writing specifications, in many cases—especially cases that involve large and complex systems, the kinds of cases for which it really matters—doing so doesn’t seem to result in much intellectual leverage, if indeed it produces any at all. This illustrates quite nicely that we often find ourselves in the position of wanting to produce epiphenomena (epiphenomena, which may be very important to us), whose formalization as an abstraction we find to be either infeasible or not particularly useful. 6.2 Bricolage as design The process of building one capability on top of another not only drives the overall increase in complexity, it also provides guidance to designers about how to do good design work. Any good designer—a developer, an architect, a programmer, or an engineer—

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knows that it is often best if one can take advantage of forces and processes already in existence as part of one’s design. But even before engineering, we as human beings made use of pre-existing capabilities. Agriculture and animal husbandry use both plant reproduction and such animal capabilities as locomotion or material (i.e., skin) production for our own purposes. The exploitation of existing capabilities for our own purposes is not a new idea. An interesting example of this approach to engineering involves recent developments in robotics. Collins reported [Collins] that a good way to make a robot walk is by exploiting gravity through what he called passive-dynamic motion—raise the robot’s leg and let gravity pull it back down—rather than by directing the robot’s limbs to follow a predefined trajectory. This illustrates in a very concrete way the use of an existing force in a design. Instead of building a robot whose every motion was explicitly programmed, Collins built a robot whose motions were controlled in part by gravity, a pre-existing force. 6.3 Infrastructure-centric development Building new capabilities on top of existing ones is not only good design, it is highly leveraged design. But now that we are aware of this strategy a further lesson can be drawn. New systems should be explicitly designed to serve as a possible basis for systems yet to come. Another way of putting this is that every time we build a new system, it should be built so that it becomes part of our environment, i.e., our infrastructure, and not just a piece of closed and isolated functionality. By infrastructure we mean systems such as the Internet, the telephone system, the electric power distribution system, etc. Each of these systems can be characterized in isolation in terms of the particular functions they perform. But more important than the functional characterization of any of these individual systems is the fact that they exist in the environment in such a way that other systems can use them as services. We should apply this perspective to all new systems that we design: design them as infrastructure services and not just as bits of functionality. Clearly Microsoft understands this. Not only does it position the systems it sells as infrastructure services, it also maintains tight ownership and control over them. When such systems become widely used elements of the economy, the company makes a lot of money. The tight control it maintains and the selfishness with which it controls these systems earns it lots of resentment as well. Society can’t prosper when any important element of its infrastructure is controlled primarily for selfish purposes. The US Department of Defense (DoD) is currently reinventing itself [Dick] to be more infrastructure-centric. This requires it to transform what is now a huge collection of independent “stovepipe” information systems, each supporting only its original procurement specification, to a unified assembly of interoperating systems. The evocative term stovepipe is intended to distinguish the existing situation—in which the DoD finds that it has acquired and deployed a large number of functionally isolated

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systems (the “stovepipes”)—from the more desirable situation in which all DoD systems are available to each other as an infrastructure of services. 6.4 Service refactoring and the age of services The process whereby infrastructure services build on other infrastructure services leads not only to new services, it also leads to service refactoring. The corporate trend toward outsourcing functions that are not considered part of the core competence of the corporation illustrates this. Payroll processing is a typical example. Because many organizations have employees who must be paid, these organizations must provide a payroll service for themselves. It has now become feasible to factor out that service and offer it as part of our economic infrastructure. This outsourcing of internal processes leads to economic efficiencies in that many such processes can be done more efficiently when performed by specialized organizations. Such specialized organizations can take advantage of economies of scale. They can also serve as focal points where expertise in their specialized service can be concentrated and the means of providing those services improved. As this process establishes itself ever more firmly, more and more organizations will focus more on offering services rather than functions, and organizations will become less stovepiped. We frequently speak of the “service industries.” For the most part this term has been used to refer to low level services—although even the fast food industry can be seen as the “outsourcing” of the personal food preparation function. With our more general notion of service in mind, historians may look back to this period as the beginning of the age of services. Recall that a successful service is an autonomous entity. It persists as long as it is able to extract from its environment enough resources, typically money, to perpetuate itself. 6.5 A possible undesirable unintended consequence The sort of service refactoring we just discussed tends to make the overall economic system more efficient. It also tends to improve reliability: the payroll service organizations are more reliable than the average corporate payroll department. On the other hand, by eliminating redundancy, efficiency makes the overall economic system more vulnerable to large scale failure. If a payroll service organization has a failure, it is likely to have a larger impact than the failure of any one corporate payroll department. This phenomenon seems to be quite common—tending to transform failure statistics from a Gaussian to a scale free distribution: the tails are longer and fatter. [Colbaugh] Failures may be less frequent, but when they occur they may be more global. This may be yet another unintended and unexpected emergent phenomenon—a modern example of the tragedy of the commons. Increased economic efficiency leads to increased vulnerability to major disasters at the societal-level. On the other hand, perhaps our growing realization that catastrophic failures may occur along with our ability to factor out commonly needed services will help us solve this

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problem as well. We now see increasing number of disaster planning services being offered.

7 Observations Our fundamental existence depends on taking energy and other resources from the environment. We must all do it to stay in existence. Raises fundamental ethical questions: how can taking be condemned? Supports stewardship notions since we are all dependent on environment. Dynamic entities are composed of static and dynamic entities (bodies and societies). That’s what makes them solid. But those static entity components are frequently replaced. Competition for energy and other resources justifies picture of evolution as survival of the meanest. Also justifies group selection since groups can ensure access to resources better than individuals.

8 Concluding remarks For most of its history, science has pursued the goal of explaining existing phenomena in terms of simpler phenomena. That’s the reductionist agenda. The approach we have taken is to ask how new phenomena may be constructed from and implemented in terms of existing phenomena. That’s the creative impulse of artists, computer scientists, engineers—and of nature. It is these new phenomena that are often thought of as emergent. When thinking in the constructive direction, a question arises that is often under-appreciated: what allows one to put existing things together to get something new—and something new that will persist in the world? What binding forces and binding strategies do we (and nature) have at our disposal? Our answer has been that there are two sorts of binding strategies: energy wells and energy-consuming processes. Energy wells are reasonably well understood—although it is astonishing how many different epiphenomena nature and technology have produced through the use of energy wells. We have not even begun to catalog the ways in which energy-consuming processes may be used to construct stable, self-perpetuating, autonomous entities. Earlier we wrote that science does not consider it within its realm to ask constructivist questions. That is not completely true. Science asks about how we got here from the big bang, and science asks about biological evolution. These are both constructivist questions. Since science is an attempt to understand nature, and since constructive processes occur in nature, it is quite consistent with the overall goals of science to ask how these constructive processes work. As far as we can determine, there is no sub-discipline of science that asks, in general, how the new arises from the existing. Science has produced some specialized answers to this question. The biological evolutionary explanation involves random mutation and crossover of design records. The cosmological explanation involves falling into energy wells of various sorts. Is there any more to say about how nature finds and then explores new possibilities? If as Dennett argues in [Dennett ‘96] this process may be fully explicated as generalized Darwinian evoEmergence Explained

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lution, questions still remain. Is there any useful way to characterize the search space that nature is exploring? What search strategies does nature use to explore that space? Clearly one strategy is human inventiveness.

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Nave, C. R., “Nuclear Binding Energy”, Hyperphysics, Department of Physics and Astronomy, Georgia State University. URL as of 6/2005: http://hyperphysics.phy-astr.gsu.edu/hbase/nucene/nucbin.html. NOAA, Glossary of Terminology, URL as of 9/7/2005: http://www8.nos.noaa.gov/coris_glossary/index.aspx?letter=s. O'Connor, Timothy, Wong, Hong Yu "Emergent Properties", The Stanford Encyclopedia of Philosophy (Summer 2005 Edition), Edward N. Zalta (ed.), forthcoming URL: http://plato.stanford.edu/archives/sum2005/entries/properties-emergent/. Prigogine, Ilya and Dilip Kondepudi, Modern Thermodynamics: from Heat Engines to Dissipative Structures, John Wiley & Sons, N.Y., 1997. Ray, T. S. 1991. “An approach to the synthesis of life,” Artificial Life II, Santa Fe Institute Studies in the Sciences of Complexity, vol. XI, Eds. C. Langton, C. Taylor, J. D. Farmer, & S. Rasmussen, Redwood City, CA: Addison-Wesley, 371--408. URL page for Tierra as of 4/2005: http://www.his.atr.jp/~ray/tierra/. Rendell, Paul, “Turing Universality in the Game of Life,” in Adamatzky, Andrew (ed.), Collision-Based Computing, Springer, 2002. URL as of 4/2005: http://rendell.server.org.uk/gol/tmdetails.htm, http://www.cs.ualberta.ca/~bulitko/F02/papers/rendell.d3.pdf, and http://www.cs.ualberta.ca/~bulitko/F02/papers/tm_words.pdf Rosen, Gideon, "Abstract Objects", The Stanford Encyclopedia of Philosophy (Fall 2001 Edition), Edward N. Zalta (ed.), URL as of 9/1/05: http://plato.stanford.edu/archives/fall2001/entries/abstract-objects/. Sachdev, S, “Quantum Phase Transitions,” in The New Physics, (ed G. Fraser), Cambridge University Press, (to appear 2006). URL as of 9/11/2005: http://silver.physics.harvard.edu/newphysics_sachdev.pdf. Shalizi, C., Causal Architecture, Complexity and Self-Organization in Time Series and Cellular Automata, PhD. Dissertation, Physics Department, University of WisconsinMadison, 2001. URL as of 6/2005: http://cscs.umich.edu/~crshalizi/thesis/single-spacedthesis.pdf Shalizi, C., “Review of Emergence from Chaos to Order,” The Bactra Review, URL as of 6/2005: http://cscs.umich.edu/~crshalizi/reviews/holland-on-emergence/ Shalizi, C., “Emergent Properties,” Notebooks, URL as of 6/2005: http://cscs.umich.edu/~crshalizi/notebooks/emergent-properties.html. Smithsonian Museum, “Chimpanzee Tool Use,” URL as of 6/2005: http://nationalzoo.si.edu/Animals/ThinkTank/ToolUse/ChimpToolUse/default.cfm. Summers, J. “Jason’s Life Page,” URL as of 6/2005: http://entropymine.com/jason/life/. Trani, M. et. al., “Patterns and trends of early successional forest in the eastern United States,” Wildlife Society Bulletin, 29(2), 413-424, 2001. URL as of 6/2005: http://www.srs.fs.usda.gov/pubs/rpc/2002-01/rpc_02january_31.pdf. University of Delaware, Graduate College of Marine Studies, Chemosynthesis, URL as of Oct 10, 2005: http://www.ocean.udel.edu/deepsea/level-2/chemistry/chemo.html

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Figures and Tables Table 1. Dissipative structures vs. self-perpetuating entities

Dissipative structures

Self-perpetuating entities

Pure epiphenomena, e.g., 2-chamber example.

Has functional design, e.g., hurricane.

Artificial boundaries.

Self-defining boundaries

Externally maintained energy gradient.

Imports, stores, and internally distributes energy.

Figure 1. Four Rayleigh-Benard convection patterns

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